Multicast replication is useful for efficiently delivering packets to a specific group of network destinations. However, unlike broadcast replication that is destined for all available destinations, multicast replication is targeted at only a certain subset of the destinations. In other words, some of the available destinations need not receive the replicated packets and can be excluded from the multicast traffic. Delivering packets to destinations that are not in the multicast group generates redundant network traffic that degrades network performance.
Even if the replicated packets were successfully limited to the destinations specified by the multicast group, multicast replication often generates redundant traffic regardless, such as when multiple copies of a same multicast packet due to network topology end up on a same network node, even though only one copy is needed.